The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
The availability of unlicensed millimeter-wave (mm-wave) radio frequency (RF) bands is spurring the development of main stream applications that use mm-wave wireless technologies. For example, the Institute of Electrical and Electronics Engineers (IEEE) 802.11ad standard, also known as WiGig, promises up to approximately 7 Gigabits per second data rate over the 60 GHz frequency band for consumer applications such as wireless transmission of high-definition video.
Wireless communication devices that operate within extremely high frequency (EHF) bands, such as the 60 GHz frequency band, are able to transmit and receive signals using relatively small antennas. However, such signals are subject to high atmospheric attenuation when compared to transmissions over lower frequency bands. In order to reduce the impact of such attenuation and boost communication range, EHF devices typically incorporate beamforming technology. For example, the IEEE 802.11ad specification details a procedure, referred to as sector-level sweep (SLS), during which a wireless station tests and negotiates the best transmit and/or receive antenna combinations with a remote station. In both a transmit sector sweep (TXSS) and a receive sector sweep (RXSS), the wireless station must switch its antenna configuration multiple times at known timing boundaries, where the switching occurs during test frame transmission for a TXSS and during test frame reception for an RXSS. The goal of the SLS phase is to identify and select an antenna configuration that allows the wireless stations to communicate at a threshold physical layer (PHY) rate.
The timing between antenna configuration switches during an SLS, as described in the IEEE 802.11ad specification, can be as short as 1 microsecond (us). Compounding the problem, beamforming during an RXSS requires the two negotiating stations to be synchronized in time such that the receiver station switches the antenna configuration right before the transmitter station starts sending a beamforming (BF) frame. Synchronization between the two peer stations is generally achieved using a timing synchronization function (TSF), where each station maintains a local TSF timer. Due to the TSF accuracy tolerance, however, the two stations' timers may vary by as much as 1 us. With a TSF accuracy of 1 us and a minimum inter-frame spacing of 1 us, timing antenna configuration changes during an SLS such that they occur at the proper times may be difficult.